The purchase of an X-ray diffractometer to be used for the study of the crystal structures of complex chemical compounds will provide essential data to further the progress of the following NIH supported investigations: 1) Reaction mechanisms and theoretical predictions of probable reaction sites on biologically active substances such as the Vitamin B12 coenzymes. 2) Predictions of stereoselectivity of useful organic reactions. 3) Study of nucleotide and oligonucleotide conformation such as the 5'-diazo-3'-acetylthymidine structure.